Cholesterol absorption and sterol balance studies have been initiated in normal subjects, in patients with hyperlipidemia and in diabetic patients with and without hyperlipidemia. The following additional measurements will be carried out in these study subjects: fasting and postprandial plasma glucose, serum cholesterol, triglycerides, quantitative lipoprotein lipid determinations, serum bile acids, fasting and postprandial insulin, glucagon, gastric inhibitory polypeptide levels, quantitative serum and urine ketones, urinary nitrogen. A total of 60 subjects will be enrolled in this study: 10 normal control subjects, 10 patients with type II hyperlipidemia without diabetes mellitus, 10 patients with type IV hyperlipidemia without diabetes mellitus, 10 diabetic patients without hyperlipidemia, 10 diabetic patients with type II hyperlipidemia and 10 diabetic patients with type IV hyperlipidemia. The data being collected will provide information regarding cholesterol absorption and cholesterol degradation in diabetic patients with and without hyperlipidemia. Such data will provide an indirect measure of the activity of the enzymes HMG CoA reductase (cholesterol synthesis) and 7-alpha hydroxylase (cholesterol degradation to bile acids). Variations in cholesteral absorption and cholesterol degradation may provide a mechanism for accelerated atherogenesis in diabetic patients with and without hyperlipidemia.